Hydropneumatic accumulators are known in a host of constructions and embodiments. One of the main tasks of hydropneumatic accumulators (accumulators) is to accommodate certain volumes of pressurized liquid of a hydraulic system and to return it if necessary to the system.
DE-A-41 31 790 discloses a bladder or membrane for an accumulator comprising an elastic material layer. The elastic material layer is laminated with a gas blocking layer. An elastic fastener is formed on the inside surface of a peripheral edge piece of the elastic material layer so that it or the material layer can be pressed onto the housing, if the fastener is attached to the housing by a holding element. The membrane is made W-shaped in cross section. The thickness of the elastic material layer decreases in an interposed section and/or increases on the curved reverse area of the material layer. The convex middle area of the W-shaped membrane is therefore reversed to the edge of the membrane. In the direction of the fastener into a concavely extending curvature and in spite of the thickness increase of the membrane intended in this area for a plurality of load cycles, its edge tearing and consequently failure of the accumulator cannot be precluded.
Conversely, in an accumulator disclosed in DE-A-40 18 318, the membrane is divided into zones which are articulated to one another to help prevent uncontrolled unfolding of the membrane during its working movements and to achieve longer service lives. In this known approach, conversely, between the deflection points of the membrane in the form of film hinges, the membrane is embossed in plate or strip form. This embossing can be unfavorable in the process of unwinding of the membrane, especially when the plate-shaped elevations abut one another. Thus, increased force application in the area of the film articulations occurs.
DE-A-1 675 349 discloses a hydropneumatic accumulator with an accumulator housing and a membrane located therein. The membrane forms a movable separating element between a first chamber, especially a gas chamber, and a second chamber, especially a liquid chamber, and has several annular areas interconnected by annular weak points which act like articulations. The annular areas have elevations on the inner side of the membrane facing away from the wall of the accumulator housing. In the central area between adjacent weak points, the elevations have the greatest height which increases the wall thickness of the membrane, and have a shape tapering off towards these weak points. Each elevation is convex at least in partial areas. In the known approach, the elevations form annular beads or ribs which project out of the plane of the separating element in the direction of the inner side of the membrane. Their convex arches taper off steeply in both directions and pass in this way into elongated annular wall areas of the separating membrane when viewed in the lengthwise direction of the hydraulic accumulator. The elongated annular wall areas keep the elevations in the initial position of the separating element at equal distances to one another. Due to the sharply delineated transitions between the bead-shaped or annular elevations and the weak points which are formed from parts of the separating element with the same wall thickness, kinks in the membrane are formed. The result is that when it moves overstresses can form locally and accordingly it can fail.